Accumulation of undesired gases is a known problem in fields such as chemical engineering and power plant operation. Gas, notably air, leaks into equipment not only operated under vacuum but even into processes operated above atmospheric pressure.
In water-steam based power plants, tray- or spray-based deaerators are used to remove air, see “deaerator” e.g. in Wikipedia. Gas removal from water is affected by making use of Henry's law, i.e. reduced gas solubility at low partial pressure, and the principle that gas solubility is reduced at higher temperatures (see e.g. www.sterlingdearator.com). Also, chemicals such as sodium sulphite can be employed as oxygen scavengers.
Numerous disclosures describe solutions of associated problems, including EP 1 829 594 (Asahi, 2004) for chemical processes, U.S. Pat. No. 4,026,111 (DOW, 1976) for removal of gas from brine for geothermal energy generation, U.S. Pat. No. 4,905,474 (steam condenser application), U.S. Pat. No. 7,588,631 (2006, vacuum deaeration by cyclones), and JP 2006 125 775 (Sanyo Electric, inventor Omori Mitsunori et al) which describes a vacuum pump solution ejecting non-condensable gases from a water/LiBr/octanol based refrigeration machine.
US 2002 000 7732 discloses membrane based separation of a working fluid in power generation from non-condensable gas.
WO 95/27 985 (Pennsylvania Power&Light Company) discusses various solutions attempted in the boiling water reactor industry, see pp. 10 chapter c.
Relevant for this invention is U.S. Pat. No. 5,487,765 (Ormat, 1994) which discloses a separate vessel comprising a membrane or diaphragm through which non-condensable gases diffuse but which retains working fluids such as lower paraffins. This solution is highly useful in an ORC process (Organic Rankine Cycle) in which a working fluid such as butane or pentane (or HCFC) is evaporated at high temperatures and condensed at lower temperature. The pressure difference between the high and low temperature sections is used to operate a turbine for electricity generation.
In energy-generation processes operated partly under vacuum, the risk of air ingress is obviously higher. The C3 process as disclosed in WO 2012/128 715 comprises a CO2 gas loop driving a turbine whereby the CO2 gas is absorbed temporarily in the cold section of the process by e.g. amines and released from said amines at higher temperatures. The process results in a thermodynamic cycle operated between e.g. 2-3 bar on the high pressure side and 0.1-0.3 bar on the low pressure side, giving a high pressure quote and a high heat-to-electricity efficiency. In this process, air ingress on the vacuum side reduces the pressure quote. Therefore, air or other non-condensable gases have to be removed from the process. At the same time, volatile amines shall not be ejected from the process.
Further to the problems not solved by prior art, pumping out residual gas, whether directly from the absorber or condenser or from a separated vessel, leads to unacceptably high removal of especially volatile working fluids, including CO2, amines, and solvents such as acetone. Therefore, a solution is desired which allows the removal of air/non-condensable gas partly at higher pressure than prevailing in the absorber section, this in order to increase the condensation of volatile working fluid, partly at lower temperature than prevailing in the absorber section, also in order to favour condensation of working fluid, and partly at minimum costs, i.e. with minimum or no investment costs especially for vacuum pumps.
Some modifications and specific embodiments of the C3 process are disclosed in documents mentioned below, all of which are included by reference.